Currently, 3rd generation cellular communication systems are being installed to further enhance the communication services provided to mobile phone users. The most widely adopted 3rd generation communication systems are based on Code Division Multiple Access (CDMA) and Frequency Division Duplex (FDD) or Time Division Duplex (TDD) technology. In CDMA systems, user separation is obtained by allocating different spreading and/or scrambling codes to different users on the same carrier frequency and in the same time intervals. This is in contrast to time division multiple access (TDMA) systems, where user separation is achieved by assigning different time slots to different users. An example of communication systems using these principles is the Universal Mobile Telecommunication System (UMTST™).
In order to provide enhanced communication services, the long term evolved (LTE) version of 3rd generation cellular communication systems are designed to support a variety of different and enhanced services. One such enhanced service is multimedia services. The demand for multimedia services that can be received via mobile phones and other handheld devices is set to grow rapidly over the next few years. Multimedia services, due to the nature of the data content that is to be communicated, require a high bandwidth. The typical and most cost-effective approach in the provision of multimedia services is to ‘broadcast’ the multimedia signals, as opposed to sending the multimedia signals in an unicast (i.e. point-to-point) manner. Typically, tens of channels carrying say, news, movies, sports, etc., may be broadcast simultaneously over a communication network. Further description of LTE, can be found in Sesia, Toufik, Baker: ‘LTE—The UMTS Long Term Evolution; From Theory to Practice’, page 11. Wiley, 2009.
As radio spectrum is at a premium, spectrally efficient transmission techniques are required in order to provide users with as many broadcast services as possible, thereby providing mobile phone users (subscribers) with the widest choice of services. It is known that broadcast services may be carried over cellular networks, in a similar manner to conventional terrestrial Television/Radio transmissions. Thus, technologies for delivering multimedia broadcast services over cellular systems, such as the evolved Mobile Broadcast and Multicast Service (eMBMS) for the LTE aspect of UMTS™, have been developed over the past few years. In these broadcast cellular systems, the same broadcast signal is transmitted over non-overlapping physical resources on adjacent cells within a conventional cellular system. Consequently, at the wireless subscriber unit, the receiver must be able to detect the broadcast signal from the cell it is connected to. Notably, this detection needs to be made in a presence of additional, potentially interfering broadcast signals, transmitted on the non-overlapping physical resources of adjacent cells.
To improve spectral efficiency, broadcast solutions have also been developed for cellular systems in which the same broadcast signal is transmitted by multiple cells but using the same (i.e. overlapping) physical resources. In these systems, cells do not cause interference to each other as the transmissions are arranged to be substantially time-coincident, and, hence, capacity is improved for broadcast services. Such systems are sometimes referred to as ‘Single Frequency Networks’, or ‘SFNs’. In SFN systems, a common cell Identifier (ID) is used to indicate those (common) cells that are to broadcast the same content at the same time. In the context of the present description, the term ‘common cell identifier’ encompasses any mechanism for specifying SFN operation, which may in some examples encompass a use of, say, a single scrambling code.
In 3GPP™ Re110 a concept 100 of relay nodes is being considered for LTE, as illustrated in FIG. 1. The relay node concept 100 involves a deployment of relay nodes (RNs) 120 that are configured/located to extend radio coverage over a Uu interface 125 to those subscriber communication units (referred to as user equipment (UE) in 3G parlance) 130 that are within the coverage area of the RN 120, but may not be in a coverage range of a serving base station, such as an evolved NodeB (eNodeB in 3G parlance). Backhaul connectivity for the RN 120 is provided using the LTE radio resource over the Un interface 115. In this manner, the RN 120 is connected over the LTE radio resource to an evolved packet core (EPC) 105 via a communication source base station (eNodeB) that (in this context) may be known as a Donor eNodeB (DeNB) 110. From a perspective of a UE 130 within the coverage range of the RN 120, the RN 120 appears as a conventional eNodeB. From a perspective of the DeNB 110, the RN 120 appears somewhat like a UE 130.
The issue of supporting eMBMS over a RN has been raised in (Tdoc R2-103960: ‘Considerations on deployment of both relay and eMBMS’. CMCC, 3GPP TSG-RAN WG2 meeting #70bis, Stockholm, Sweden, 28 Jun.-2 Jul. 2010). In this document a method for extending eMBMS was briefly described:                ‘Under this architecture, the content synchronization should be guaranteed not only from BM-SC to DeNB, but also from BM-SC to RN. In this case, the eMBMS related data needs to be transmitted to the DeNB firstly, and then be forwarded towards the corresponding RNs before transmitting to the UEs.’        
This extract clearly suggests to those in the art that the Donor eNodeB 110 would first forward eMBMS traffic from the DeNB 110 to the RN 120 using a unicast bearer, although no bearer is specified. Once the RNs 120 have received the eMBMS data then both DeNB's 110 and RN's 120 can transmit the eMBMS data over the single frequency at the same time, such that UE's 130 can easily combine at the physical layer the transmissions from all eNodeB's and RN's 120 within range. With any RN approach it is very important that the RN 120 decodes the MBMS traffic received from the DeNB 110 over the Un 115 as accurately as possible since the RN 120 may be re-broadcasting this information to many 10s of UEs 130 over the Uu 125. Very few solutions have so far been described or discussed to address this need.
Consequently, current techniques are suboptimal. Hence, an improved mechanism for improving a probability of correct detection of an MBMS signal at the RN in a cellular network that uses a RN concept would be advantageous.